1. Field of the Invention
The present invention relates to a printer in which an ink-jet recording method is employed in order to jet ink onto, e.g., the surface of a recording paper and more particularly, to an ink-jet printer which enables the improvement of impact-errors and dot-defects during printing.
2. Description of the Prior Art
In recent years, ink-jet printers using an ink-jet device have shown a tendency to have colorizedation facilities and have high quality images. Dots, which are jetted on a recording paper, are required to be highly densified in order to further improve resolution, or heads are required to be arranged in a highly dense formation to miniaturize their dimensions. In addition, the amount of an ink drop to be jetted is also required to be reduced.
FIG. 3 shows a partly diagrammatic sectional view of a prior art ink-jet head. FIG. 4 shows a sectional view taken on line A--A of the ink-jet head in FIG. 3.
As shown in FIGS. 3 and 4, the ink-jet head comprises a flow passage member 8 and a base plate 5. The flow passage member 8 is provided on the upper surface of the base plate 5. An ink supply hole 6 and flow passages 7 are formed in the flow passage member 8. Heaters 4 are provided in the base plate 5. A nozzle plate 3 is fixed on the upper surface of the flow passage member 8 with an adhesive 13. Nozzle holes 2 for jetting ink 1 are formed in the nozzle plate 3. When a voltage is applied to the heaters 4 from a voltage supplying device 9, the heaters 4 heat the ink 1 so that boiling bubbles 10 are formed in the ink 1. As a result, an ink drop 12 is jetted toward a recording paper 11 through one of the nozzle holes 2.
Each of the nozzle holes 2 formed in the nozzle plate 3 has a circular opening. Heretofore, the nozzle holes 2 are formed by a laser processing or an electroforming processing. Such an ink-jet head is used by being incorporated into a conventional ink cartridge, then this ink cartridge is installed in a printer.
An operation and an outline of a printing gist of the ink-jet printer having an arrangement as mentioned above are as follows.
When the heaters 4 abruptly heat the ink 1 by electrifying the heaters 4, boiling bubbles 10 are formed in the ink 1 and then the ink 1 existing in flow passages 7 which leads to portions facing the nozzle holes 2 is pressured to flow toward the nozzle holes 2. Then, a portion of the ink 1 flies out of the nozzle holes 2 into air so as to form the ink drop 12 by means of the surface tension which acts on the ink 1 and then adheres to the recording paper 11.
On the other hand, the boiling bubbles 10 which have been boiled are cooled by the ink 1 existing in the flow passages 7 to abruptly decrease its volume. By a negative pressure occuring on the volume decrease of the boiling bubbles 10 and by the surface tension which acts on the ink 1, the ink 1 is recharged through the ink supply hole 6 and the flow passages 7.
By repeating t he above-mentioned operation, in response to a printing signal sent from a computer or the like, the voltage supplying device 9 applies a driving revoltage to each of any arbitrary heaters 4 among the heaters 4 in alignment with the position of a carriage of the ink-jet printer, so that the ink drop 12 is successively generated. By such a control and an operation, a portion of the ink 1 is adhered to the recording paper 11 which is fed by a platen roller of the ink-jet printer, thereby enabling the printing by means of dots.
In order to obtain a high quality resolution, the interval between the dots is made to be 42.3 .mu.m which is nearly half of 84.7 .mu.m (in the case of 300 dpi), i.e. 600 dots per inch (in the case of 600 dpi). The dot diameter (i.e. the diameter of each of the dots) is miniaturized from 120 .mu.m to 60 .mu.m and the amount of the ink drop is reduced to 20 pl or so which is nearly not more than 1/3 of that of a conventional ink-jet printer.
As described above, the nozzle holes 2 of the nozzle plate 3 are formed by a laser processing or an electroforming processing. Since the inside diameter of each of the nozzle holes 2 is so minute, it is difficult to roundly process each of the nozzle holes 2 with a high accuracy. If burrs, processing-strains (strains caused by processing) and the like are formed in the nozzle holes 2, it becomes a great hindrance when printing i.e. jetting the ink drop in an appropriate direction.
FIGS. 5A and 5B shows schematic views illustrating such phenomena. FIG. 5A shows a sectional view illustrating a deviation of the ink drop due to a processing-strain formed in one of the nozzle holes. FIG. 5B shows a plan view illustrating a profile of one of the nozzle holes.
There is a recessed portion 2a in a part of the inside circumference of one of the nozzle holes 2. The part of the inside circumeference is outwardly deformed due to a processing-strain caused when forming the nozzle holes 2. Owing to the presence of such a recessed portion 2a, an ink portion 23 just before being jetted tends to deform toward the direction of the recessed portion 2a as shown in FIG. 5A. Thus, an impact position of the ink portion 23 is deviated from a correct position to be impacted on the recording paper 11.
That is to say, when jetting an ink drop whose amount is extremely more minute than that of a conventional ink drop in order to achieve a higher resolution, the inertia force which acts on the ink drop is smaller than that of the conventional ink drop so that the ink drop is apt to be affected by the surface tension which acts on the ink portion 23. For this reason, if the recessed portion 2a as shown in FIG. 5B remains as a result of a processing-strain, the ink portion 23 is forced to be attracted toward the side of the recessed portion 2a. Accordingly, impact-errors (i.e. a jetted ink drop 24 impacts a wrong position deviated from a desired correct impact position) thereby causing a problem that the printing quality is considerably deteriorated.